The history of steam road vehicles describes the development of vehicles powered by a steam engine for use on land and independent of rails; whether for conventional road use, such as the steam car and steam waggon, or for agricultural or heavy haulage work, such as the traction engine.

The first experimental vehicles were built in the 17th and 18th century, but it was not until after Richard Trevithick had developed the use of high-pressure steam, around 1800, that mobile steam engines became a practical proposition. The first half of the 19th century saw great progress in steam vehicle design, and by the 1850s it was viable to produce them on a commercial basis. The next sixty years saw continuing improvements in vehicle technology and manufacturing techniques and steam road vehicles were used for many applications. In the twentieth century, the rapid development of internal combustion engine technology, coupled with adverse legislation, led to the demise of the steam engine as a source of propulsion of vehicles on a commercial basis, with relatively few remaining in use after the Second World War. However, many vehicles were acquired by enthusiasts for preservation, and numerous examples are still in existence. Moreover, the threat of Global Warming, and the search for renewable energy sources, has led to a resurgence of interest in utilising steam as a power source for road vehicles in the future.

Early research on the steam engine before 1700 was closely linked to the quest for self-propelled vehicles and ships; the first practical applications from 1712 were stationary plant working at very low pressure which entailed engines of very large dimensions. The size reduction necessary for road transport meant an increase in steam pressure with all the attendant dangers, due to the inadequate boiler technology of the period. A strong opponent of high pressure steam was James Watt who, along with Matthew Boulton did all he could to dissuade William Murdoch from developing and patenting his steam carriage, built in model form in 1784.

Ferdinand Verbiest is suggested to have built what may have been the first steam powered car in about 1672, but very little concrete information on this is known to exist. During the latter part of the 18th century, there were numerous attempts to produce self-propelled steerable vehicles. Many remained in the form of models. Progress was dogged by many problems inherent to road vehicles in general, such as suitable power-plant giving steady rotative motion, suspension, braking, steering, adequate road surfaces, tyres, and vibration-resistant bodywork, among other issues. The extreme complexity of these issues can be said to have hampered progress over more than a hundred years, as much as hostile legislation.

More commercially successful for a time than Trevithick’s carriage were the steam carriage services operated in England in the 1830s, principally by Walter Hancock and associates of Sir Goldsworthy Gurney, among others. However, the heavy road tolls imposed by the Turnpike Acts discouraged steam road vehicles and for a short time allowed the continued monopoly of horse traction until railway trunk routes became established in the 1840s and ’50s.

Although engineers developed ingenious steam-powered road vehicles, they did not enjoy the same level of acceptance and expansion as steam power at sea and on the railways in the middle and late 19th century of the “Age of Steam”. Harsh legislation virtually eliminated mechanically propelled vehicles from the roads of Great Britain for 30 years, the Locomotive Act of 1861 imposing restrictive speed limits on “road locomotives” of 5 mph (8 km/h) in towns and cities, and 10 mph (16 km/h) in the country. In 1865 the Locomotives Act of that year (the famous Red Flag Act) further reduced the speed limits to 4 mph (6.4 km/h) in the country and just 2 mph (3.2 km/h) in towns and cities, additionally requiring a man bearing a red flag to precede every vehicle. At the same time, the act gave local authorities the power to specify the hours during which any such vehicle might use the roads. The sole exceptions were street trams which from 1879 onwards were authorised under licence from the Board of Trade.

In France the situation was radically different from the extent of the 1861 ministerial ruling formally authorising the circulation of steam vehicles on ordinary roads. Whilst this led to considerable technological advances throughout the 1870s and ’80s, steam vehicles nevertheless remained a rarity. To an extent competition from the successful railway network reduced the need for steam vehicles. From the 1860s onwards, attention was turned more to the development of various forms of traction engine which could either be used for stationary work such as sawing wood and threshing, or for transporting outsize loads too voluminous to go by rail. Steam trucks were also developed but their use was generally confined to the local distribution of heavy materials such as coal and building materials from railway stations and ports.